Much of the epic progress during the industrial revolution in the United States during the 19th and 20th century was powered by steam. However, the thermal efficiency of steam powered piston engines could not match that of the Otto or Diesel engines developed at the end of the 19th century. A substantial improvement in steam engine efficiency was however made when the uniflow steam engine was developed by Professor Stumpf in Germany and improved further in the U.S. by C. C. Williams high compression uniflow engine based on compression as described in U.S. Pat. Nos. 2,402,699 and 2,943,608 in which steam is compressed to boiler pressure by the piston return stroke thereby raising the steam temperature for example 95 to 342 degrees hotter than feed steam in a sizeable clearance volume that may be 7% to 14.5% of displacement. The thermal efficiency of even these engines while improved, could not however reach that of the internal combustion engine.
Recently, a substantial further advance has been made through the development of steam engines operating on a cycle that employs essentially zero clearance between the piston and the cylinder head at the end of the exhaust stroke while at the same time any steam in the cylinder is under zero compression; a Z-Z operating principle. This arrangement achieves a remarkable increase in thermal efficiency as disclosed in U.S. Pat. Nos. 8,448,440, 9,316,130, 8,661,817, 9,828,886 and pending U.S. patent application Ser. No. 15/794,486 filed Oct. 26, 2017, now U.S. Pat. No. 10,273,840 all of which are assigned to the Applicant's assignee and incorporated herein by reference. Engines described in the latter five patents listed above provide a thermal efficiency which ranges from an improvement of about 15% to an extraordinary 59% better than the best performing high compression uniflow engines which are widely recognized to have the highest thermal efficiency of any steam engine previously known (see FIG. 1). The outstanding efficiency of the engines built according to the Z-Z patents listed above results from several factors including the Z-Z operating principle as well as benefits arising from the use of a unique, fast acting inlet valve which can open fully in some embodiments in less than 1 millisecond thereby avoiding losses formerly caused by a restriction in the flow of steam (also sometimes called “wire drawing”) through the steam inlet valve while the valve is being opened by a cam or eccentric which may take as much as ⅓ to ½ of a crankshaft rotation resulting in reduced efficiency and power output. By contrast, since the inlet valve of Z-Z engines of the present invention is opened fully almost instantly while the piston clearance is virtually zero, work output begins at the highest steam supply pressure earlier in the cycle thereby providing more power while also eliminating losses associated with having to compress to supply pressure a substantial quantity of steam that remains in the cylinder. One aim of the present invention is to be able to achieve these advantages disclosed in the Z-Z patents listed above.
While efficiency has been greatly improved in the five patents listed, several deficiencies were discovered. Valve springs when overheated can lose their temper preventing peak performance. Fiber packing and other nonmetallic seals can create friction or become worn and leak. Valve lifters (projections between a valve and the piston) used to push valve open by piston motion can become weakened due to progressive fracture under cyclic loading over time.
In view of these and other deficiencies it is therefore one object of the present invention to retain the high efficiency and other advantages of the Z-Z engine patents noted above while actuating one or more valves by piston movement with little or no wear even when opening or closing the valve in under 1 millisecond.
Another object is to yieldably bias inlet and exhaust poppet valves without the need of springs.
Another object is to extend the working life of the engine valves subject to progressive fracture under cyclic loading while reducing the reciprocating mass of the valves and valve train.
Still another object is to find a way to retain the high thermal efficiency advantages of a zero clearance with zero compression operating principle while reducing the mass of a reciprocating valve train that includes one half the mass of the valve spring.
Another object is to eliminate or reduce leakage of working fluid while providing a way of actuating a steam inlet or exhaust valves without a camshaft system by timing at least one steam valve electrically using a computerized electric engine control unit (ECU) and without the necessity of forming valves from a ferromagnetic material.
It is a more specific object to maintain the high thermal efficiency that characterizes the virtual zero or near zero clearance with zero or near zero pressure steam cycle of U.S. Pat. Nos. 8,448,440, 9,316,130, 9,828,886 and Ser. No. 15/794,486, now U.S. Pat. No. 10,273,840 wherein steam admission is accurately timed and cut off automatically at any selected time using a relatively low mass steam inlet valve that is able to reciprocate at over 50 cycles per second without the need of a spring, cam shaft assembly or eccentric system and without a valve lifter on the piston that contacts the valve to push it open or closed.
Another object is to hold exhaust valves closed reliably yet assure that they can be opened with a small amount of valve work that does not significantly reduce thermal efficiency so as to thereby achieve higher overall thermal efficiency than the best reciprocating steam engines currently in commercial use.
These and other more detailed and specific objects and advantages of the present invention will be better understood by reference to the following figures and detailed description which illustrate by way of example but a few of the various forms of the invention within the scope of the appended claims.